I decided to build a Fuzz Face clone, to see what all the fuss (no pun!) was about, as I'm not a fuzz user myself.
I used the directions from Phillip's Fuzzcentral stuff, but I wanted it to be NPN, so I switched the polarity of the electrolytics and the -9V did become +9V.
I used a 1k lineair pot for Fuzz, 500k log for Volume,
2x AC127 NPN Ge transistors and kept the rest of the stuff original (2.2uF and 22uF electrolytics, resistors 33k, 100k, 470 Ohm and 8k2).
I did bias one of the AC127's, by raising the 8k2 to 12k. This gave 4.69V across the collector/+9V (whereas it was 3.97V with the 8k2)
So far so good right?
Not really. While the fuzz works as it should (turn fuzz clockwise=more fuzz, turn volume clockwise=more volume), there are 2 very strange things happening:
1) As the Fuzz control is being increased, the volume drops. And once it's past '2 o' clock', the volume DIVES way below unity gain. Yes, there IS more fuzz happening, but you can hardly hear it, even with the volume cranked.
2) When I roll back the tone knob of my guitar, I expected a more round singing fuzz sound. But it become brighter/clearer and more fuzzy. ??? ??? ???
Does anyone have any clue what might be wrong here?
I double checked all the wires/connections already (although I did build it on perfboard) and I even swapped the '1' and '3' wires of the Fuzz-pot, which just reversed the problem.
Do a resistance check on the 1k pot. Does it transistion normally? Are there any changes drastically when you move any of the lugs under test? Let me know the results.pl
Sounds like the pot is not working right!!! Â You can check this by simulating the pot with a 1 K resistor.....hooked up as if where maxed to full fuzz and see what kind of volume you get than...that is what I would do!!!
 The pot may have some solder in it that is common to happen......
Quote from: Pedal love on December 22, 2005, 07:42:17 PM
Are there any changes drastically when you move any of the lugs under test? Let me know the results.pl
What do you mean with 'move any of the lugs'? I mean, the pot is screwed tightly in its hole and none of the lugs are close to the enclosure or anything.
It's an Alpha pot btw, but since it's almost 2am here, I'm going to have to wait 'till tomorrow to change it.
By the way, is it normal for a Ge Fuzz Face to change 'face' drastically when you use your 5-way switch in a HSH equipped guitar?
The fuzz becomes more prominent with singlecoils it seems.
I would substitute the 1k pot for another 1k pot for it is obvious to me that this pot or the bypass 22uf capacitors, malfunctioning or not connected somewhere properly.pl
Check the 1k pot, check the 22uf capacitor, make sure everything is connected together correctly and try it again.pl
Quote from: Pedal love on December 22, 2005, 08:29:29 PM
Check the 1k pot, check the 22uf capacitor, make sure everything is connected together correctly and try it again.pl
I checked the 1k pot, and it behaves totally normal (down from 0.3 Ohm up to 1.028k Ohm)
How to check the big cap then? My DMM only has 2 modes for capacitors, one is up to 4nF and the other up to 400nF. :'(
Does the ECB order change when converting a PNP Fuzzface to a NPN perhaps?
When changing from NPN to PNP you have to go from negative ground to positive, and turn all caps around...thats really it though. (AFAIK)
Pedal Love's got it. Likeliest cause for what you describe is first a shorted or reversed polarity 22uF cap, then a bum or wrong-value 1K pot. Or both. There are others, but check those first.
http://www.generalguitargadgets.com/diagrams/fuzzface_sc_nn.gif
Here's a great place to start, or choose another correct one for your transistors.
I swapped the 22uF electrolytic for a 15uF one, but the problem remained.
I got so fed up with this (soldering on perfboard is a bitch), I socketed the electrolytic.
Went back and forth between the 2, but the weird problem remains.
I'm really out of ideas. :'( I checked all the connections. They all seem good (because the fuzz also works normally, apart from the drop in volume, when the fuzz control is increased.
I checked it with 9V PSU and battery; problem remains.
These are the moments I really hate electronics/DIY. If only it WAS a bad pot or a bad cap, then I could blame the parts.
Oh, I previously checked with different transistors as well (BC109C, N3904 and now AC127 and AC141). The problem remains. :icon_frown:
OK, not the obvious problem then.
What do the collector voltages do as you turn the pot?
Quote from: R.G. on December 23, 2005, 10:53:00 AM
OK, not the obvious problem then.
What do the collector voltages do as you turn the pot?
From which transistor? (I have to measure between Collector and +9V right?)
Both collectors, measure between collectors and ground.
Aren't you Mr. Hot Wire Audio man? Why are you asking for help in a DIY forum?
Even if you've double checked that pot, replace it if you haven't already. I had a similar problem with a 2k pot (in a Fuzz Face, no less), checked out fine with a meter but something was funny with it. One of the lug traces was bad/intermittent.
Quote from: cd on December 23, 2005, 11:38:54 AM
Aren't you Mr. Hot Wire Audio man? Why are you asking for help in a DIY forum?
:-\ Yes I am. And perhaps because there are tons of more knowledgeable people on this board.
Like I said, this is my first endavour with a DIY fuzz (and transistors for that matter, since the pedals I built before all work with op-amps).
But if you happen to have a problem with me posting here, I'll be happy to hear it. ::) :icon_wink:
Quote from: R.G. on December 23, 2005, 10:58:01 AM
Both collectors, measure between collectors and ground.
O.k., just measured them. I dunno if the behaviour is strange or not, but these are the results:
Fuzz knob @ 0%. Q1 C = 0,438V; Q2 C= 4,51V
Fuzz knob @ 50%. Q1 C = 0,438V; Q2 C= 4,51V
Fuzz knob @ 100%. Q1 C = 0,438V; Q2 C= 4,51V
BUT... While I was measuring, steadily the Q2 C voltage was rising. At the start of the test it was around 4,47V, and at the end it was around 4,88V (!!!). And the Q1 C voltage was slowly dropping (from 0,438 down to 0,423V).
So, while the Fuzz knob didn't change the readings, the readings themselves were slowly changing. (like 0,01V rise each 3 or 4 seconds).
Just checked again. Now the Q2 voltage was all the way up to 6,7V and DROPPING, and the Q1 C voltage was down to 0.267V and RISING! ???
A bad cap somewhere or something?! ??? :icon_frown:
QuoteA bad cap somewhere or something?!
Affirmative. Check all the electros. A leaky or reversed input cap might do something like that.
R.G., I just replaced BOTH the electrolytics AND the transistors (N3904 Si instead of the NPN Ge AC141's).
The problem remains. The voltage ramps up and down slowly.
I think you might have the polarity on the caps backwards.
Built on perf, right? Have you checked your solder joints with a good magnifying glass for cold or bridged joints? I'd give that a try, plus it wouldn't hurt to re-flow all the solder joints either.
Quote from: Joecool85 on December 23, 2005, 01:39:36 PM
I think you might have the polarity on the caps backwards.
No, I did that one time on accident when I replaced the 22uF with a 15uF (because the 15uF doesn't have a minus-symbol, but a narrowing of the enclosure, while the plus-side has a black stripe, so I figured that would be the minus-side) and then there's a very faint, ugly signal, which is totally different from what I'm experiencing when I got the caps right.
@FW; I did check them several times and I also made sure to go through 'alleyways' with a knife, between solder-'heeps', so that 2 different things couldn't connect.
I'm getting a PCB after X-mas I think, so I'll transfer all the parts to that, see if it matters. But I'm really at a point that I could toss the whole thing out the window. :-[
Thats what happened with mine. I was ticked. I grabbed a new board, soldered it all in, and it worked! I think I had a short somewhere on mine I was overlooking. Something to think about.
wait a minute you said q1's collector was 4.5 volts? did you mean q2? if its the first transistor, check to make sure the resistor going to q1's collector is indeed the value specified, check it with your meter. q1's collector should be like 1v or slightly higher. coudnt hurt anyways...
hope this helps
Brent
I had a weird problem like this. The pedal worked normally and then the voltages would start rising on the tranistors untill the pedal wouldnt work. It turned out I hadnt hooked up a ground wire to one of my pots :-[ It has been working eversince ;D
Quote from: cmat on December 24, 2005, 12:39:30 AM
I had a weird problem like this. The pedal worked normally and then the voltages would start rising on the tranistors untill the pedal wouldnt work. It turned out I hadnt hooked up a ground wire to one of my pots :-[ It has been working eversince ;D
Right now I have 2 seperate ground wires from the board to the pots and from the volume pot to the 9V input jack.
@b_rogers:
Yeah I ment Q2. While Q2 was rising from 4,5V upwards, Q1 was dropping from 0,438V downwards. I haven't checked the 2 AC141's properly for leakage, but the problem was the same with different (silicium) transistors as well. ???
Do those two ground wires connect? They should.
I'd like to see a chosen schematic, and transistor type [npn/pnp].
Also complete pin voltage information [EBC readings from both Q's].
And battery supply measured voltage to reference the pin voltages by.
Quote from: petemoore on December 24, 2005, 11:54:14 AM
 I'd like to see a chosen schematic, and transistor type [npn/pnp].
 Also complete pin voltage information [EBC readings from both Q's].
 And battery supply measured voltage to reference the pin voltages by.
Hi, I based it on the schematic posted on http://fuzzcentral.tripod.com/fuzzface.html
transistor type = NPN
Batt. supply voltage = 9.32V
Also complete pin voltage information [EBC readings from both Q's].
From ground, take a voltage measurement with DMM from Q1 Emitter, base and collector, also Q2's Emitter, base and collector, post them here.
NPN Neg Gnd FF schematic...
They are probaly 'normal npn's, so looking at the top of the board with input to the left/output to the right... the emitters would be on the 'bottom', bases in the middle, and collectors nearest V+, the transistor markings would be facing the output...or verify pinouts to board connections by inspecting the board connections, comparing them to the schematic, also transistor data sheet.
transistor mis-pinout
is a common miswire for FF's....something to recheck at least.
Hey Pete, the PCB's arrived, so I immediately populated them and threw one into the enclosure.
It WORKS!
And what a tone too. With my Burny Les Paul Custom (Randy Rhoads model), GFS Vintage '59 Alnico PAF neck and GFS Crunchy PAF bridge, I pretty much nailed the Guess Who-"American Woman" tone (both lead and rhythm).
I put 2 N3904's in there (hFE around 240-250) and with the fuzz control (1k lineair) maxed, it has this saturated, singing, violin/fuzz tone.
HOWEVER... Is it normal for a Fuzz Face circuit to have the biggest change in fuzz intensity in the last quarter of the 1k lineair potmeter?
Or should I try 1k log or 1k reverse log?
Also, with some guitars, the fuzz had a sort of switch-point, when you roll back the volume. Below it's crunchy overdrive and above it hits into the fuzz. It's not gradually. But, when you put a buffered pedal in front of it (off), that problem is gone.
Any idea if that behaviour is normal?
Or is there a treshold voltage that the N3904's need?
the "switch point" you refer to is pretty normal. with the FF's i have made the transistion is more gradual with strats than humbucker guitars. germanium cleans up better, but silicon to my ears sounds better. the pot bunch up at the end is also normal, i usually omit the pot and just use a 1k resistor to ground and the guitar vol becomes the pot (sort of) Fuzz faces rule! altho i admit i like mine best into a ts style circuit. try the multi face at runoff groove for hours of fuzz tweaking.
enjoy!
Small Bear sells the wierd taper 1k Fuzzpot for the circuit, makes it very evenly ranged to dial in the Gain. I add a small stop resistor [100 ohm or better] to match the gain I want for that one, if it needs it.
Maybe a resistor at the input, or input gain control would change the way your guit's volknob works, tame the FF a bit, maybe even keep some noises out.
Sounds like you're using different pickups, you can put the input gain mod on a switch or use a pot.
Hey Pete, where would you place the resistor then? Before or after the 2.2uF electrolytic?
And the value? Something like 1 or 2 Mega Ohm?
Small Bear sells the wierd taper 1k Fuzzpot for the circuit, makes it very evenly ranged to dial in the Gain. I add a small stop resistor [100 ohm or better] to match the gain I want for that one, if it needs it.
"Pete, where would you place the resistor then".
If you check out Joe Davissons FF calc, you'll see that FF's can use tweeking of the gain pot value. This bears out in practice, too large [2k2?...5k?], starts messing with the bias and sound too much, I decided it's worth it to just 'set' the value of the gain resistor [or pot].
a 2k2 pot produces more gain than a 1k, so...setting the pot to a 'middle-er] position also puts resistance between the 22uf and feedback loop [100k].
I used to start with a 2k2 adjusted fully Cw [max] and 'work down' the value [actually using another pot, 5k or so, clipped across the 2k2's outer lugs], set max gain at 'whatever'...not oversaturated, just a touch more than you'd use...depending about pickups etc.
Measure the removed/undisturbed setting you liked on the 5k, replace with same value fixed resistor where the 5k was used to find the value across the 2k.
Now, since I have access to the 'correct' pot from SB, I insert an R value between the gain pot and ground to increase max gain to where I want it. Starting with the SB 1k FF pot, Fully Cw, but splicing a 1k lin. pot between the SB gainpot and ground, setting max gain, and replacing the 'R value finder' pot with a fixed resistor of nearest same value, maybe having to build the fixed R value from resistors [to more closely match the target value.
"I'm calling it 'floating' the pot...[stop resistor is the term tho] min. gain will be 'bumped up' as will max gain. ...the gain range adjustment is 'moved up' by the gain bumping resistor, between the gain pot and ground....something between 100 ohm and 1k, or to taste.
This might not be necessary for Si or some FF's, A 1k gainpot might even be more than you want.